The objective of this proposed research is to determine factors which influence release of pituitary hormones in response to PGF2 alpha in cattle. To test whether LH is released in direct response to PGF2 alpha or indirectly in response to gonadal hormone changes induced by PGF2 alpha, blood LH will be determined in prepubertal and postpubertal males and females (intact and castrate) treated with PGF2 alpha. In addition, gonadal steroids will be implanted in cows in diestrus in an effort to block the minor acute surge as well as the ovulatory surge of LH which follow treatment with PGF2 alpha. The influence of PGF2 alpha on LH release caused by GnRH will be determined. Blood growth hormone, prolactin and glucocorticoid will be assayed in the same animals to determine specificity of the LH responses. An effort will be made to block prolactin release in response to PGF2 alpha by pretreatment with ergocryptine, the elevation in growth hormone by pretreatment with somatostatin, and the elevation of glucocorticoid in response to PGF2 alpha by pretreatment with dexamethasone.